Image inspect non-app CNABs

[zappy-shu]

- What I did

Allow image inspect of CNABs not created with docker app. The command will output basic information that is read from the bundle.json file including:

• metadata (version, name, description, maintainers)
• services (name and image)
• parameters (including default values if present)

Metadata fields are now printed in PascalCase to match the other fields

- How I did it

The image inspect command first checks if the invocation image supports the custom com.docker.app.inspect command. If yes then this is called with the format as before. If not then it's not a Docker App bundle and the bundle file is parsed for the relevant information which is then printed using the same formatters as the Docker App inspect function.

- How to verify it

Manually create a CNAB, push it to hub with cnab-to-oci, and pull it with docker app. Use docker app image inspect <cnab-id> and confirm the output contains the metadata, services, and parameters.

You can also use docker app image inspect <cnab-id> --pretty to get a table view but 2 fields are removed (REPLICAS and PORTS)

- Description for the changelog

Allow docker app image inspect of CNAB bundles created without Docker App

- A picture of a cute animal (not mandatory)

[codecov[bot]]

Codecov Report

Merging #753 into master will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #753   +/-   ##
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  Coverage   69.94%   69.94%           
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  Files          63       63           
  Lines        3540     3540           
=======================================
  Hits         2476     2476           
  Misses        744      744           
  Partials      320      320

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